With 5W- oil in it and hot, I get about 25 P.S.I. at idle. It cracks at about 40 when at speed. I haven't looked at the insides of mine, because it doesn't leak, but I use full synthetic and doubt it has any build-up at all. It's very important to change oil and filter regularly and have a good 210 degree thermostat to keep sludge to a minimum. If your engine runs cooler, you will need to change oil sooner.